Combined load-equalizing and safety device for lifts



J 12 1956 J. B. HARRISON 2,750,004

COMBINED LOAD-EQUALIZING AND SAFETY' DEVICE FOR LIFTS Filed April 9, 1952 2 Sheets-Sheet 1 J1me 1956 J. B. HARRISON COMBINED LOAD-EQUALIZING AND SAFETY DEVICE FOR LIFTS 2 Sheets-Sheet 2 Filed April 9, 1952 United States Patent COMBINED LOAD-EQUALIZING AND SAFETY DEVICE FOR LIFTS John Bertram Harrison, Memphis, Tenn., assignor to Dover Corporation, a corporation of Delaware Application April 9, 1952, Serial No. 281,436

7 Claims. (Cl. 187-85) This invention relates to safety devices for use with elevators, automotive lifts, and the like, and more particularly to a combination of load equalizing mechanism with means for preventing possible dangerous lowering of the lift in the event of failure of the elevating means. Although the invention may be embodied in other types of lifts and elevators, it has particular advantage when used on those which are hydraulically operated, and it is therefore shown and described as a part of an elevator of this type.

A principal object of the invention, therefore, is to provide mechanism for maintaining the lift platform level under all conditions of load, and means associated therewith for preventing lowering of the lift except upon manual release of said means.

Other objects will appear from the following description, reference being had to the accompanying drawings, in which Fig. 1 is an elevational view (with a few parts shown in section) of one embodiment of the invention as applied to a twin post lift operating at and above floor level;

Fig. 2 is a similar View of another form of the invention as applied to a single post lift operating in a pit;

Fig. 3 is, in general, an elevational view of a further modification, a few parts being shown in section;

Fig. 4 is a vertical sectional view, taken on the line 4-4 of Fig. 3;

Fig. 5 is generally an elevation of another embodiment of the invention; and

Fig. 6 is a vertical sectional view, taken on the line 6-6 of Fig. 5.

In Fig. l, the twin post lift comprises a pair of cylinders 10 with plungers 12 each reciprocable in its respective cylinder 10, plunger heads 14 and 15, and a platform or runways 18 carried by the plunger heads 14 and 15. The cylinders 10 are supplied with hydraulic operating fluid under pressure by known means, including suitable control valves. An unequally distributed load 20 is shown resting on a platform 18 of the lift. At the bottom of a shallow pit 22, which is provided with a cover 24, are pairs of fixed brackets 26 supporting shafts 28 and 29. Two sprocket wheels 30 are mounted for free rotation on shaft 28. These sprockets should also rotate freely relative to one another to enable the chains to be adjusted. Two sprocket wheels .32 are similarly spaced apart and mounted for rotation on a shaft 29 carried by a bracket 26. These sprockets are rigidly secured together and have a ratchet wheel 34 secured to them by a plurality of bolts 33.

Rigidly secured to the plunger heads 14 and (Fig. 1) are channels 36 and 38. One end'of a chain 40 is secured to the plunger head 15 at the upper end of the channel 36, while its other end is secured to the lower end 42 of the channel 38. Intermediate its ends, the chain 40 passes in meshing engagement with a first member of each of the paired sprockets 30 and 32. Similarly, one end of a chain 44 is secured to the plunger head 14 at the upper end of the channel 38, while its other end is secured to the bottom 46 of the channel 36, the chain 44, intermediate its ends, passing in meshing engagement with the second member of each of the paired sprockets 30 and 32.

A pawl 48 is pivotally secured to a plate 50 by a stud 52. The tooth of the pawl 48 may be moved by gravity into engagement with the ratchet wheel 34, and may be manually disengaged by pulling on a handle 53 attached to the pawl by a rod or wire cord 54 which extends through the pit cover 24 and a tension spring 55. A stop stud 56 limits clockwise movement of the pawl. When the platform 18 reaches the end of a normal downward movement of the lift, the pawl 48 is reset into operative engagement with the ratchet wheel 34 by a cam 58 carried by the plunger head 14.

The form of the invention illustrated in Fig. 1 causes load equalization on the two plungers 12 by virtue of the criss-cross arrangement of the chains 40 and 44, and by their meshing with the sprockets and the platform 18 is therefore maintained level. In addition, accidental downward movement of the lift platform is prevented by the engagement of the pawl 48 with the ratchet wheel 34, the lift being supported by the portions of the two chains which are in mesh with the sprockets 33 and which extend to the lower anchorages 42 and 46.

When the load is to be lowered, the handle 53 is pulled to raise the pawl 48 from the ratchet wheel 34. If some of the hydraulic fluid has leaked from the cylinders 10 and the pawl 48 is in engagement with the ratchet wheel 34, it may not be possible to disengage the pawl because the pawl is, in effect, carrying the load. Under these unusual conditions, sufficient hydraulic fluid is supplied to the cylinders 10 to permit the pawl 48 to be disengaged from the ratchet wheel. Thereafter the usual lowering valve is opened to allow the lift to descend. To avoid the necessity of holding the handle 53 during the lowering of the lift, the pawl 48 is suitably weighted so that it will remain against the stop 56 due to the force of gravity acting on its upwardly extending portion, or the cord or rod 54 may be in frictional engagement with the pit cover 24.

The mode of anchoring of chains 40 and 44, and the manner in which they pass around their respective sprockets 30 and 32, are such that the plungers 12 are lowered at the same rate, and the platform 18 is maintained horizontal at all times.

The single post lift of Fig. 2 is shown as installed in a pit 60, having suitably heavy side walls 61. The lift comprises a cylinder 62, a plunger 64 reciprocable therein, and a platform 66 mounted on the plunger 64. A pair of sprocket wheels 68, suitably spaced apart, is mounted for independent free rotation on a shaft 70 carried by a pair of plates 72 secured to and extending below the platform 66. A second pair of sprocket wheels '74, also suitably spaced apart but rigidly connected together, is mounted for free rotation on a shaft 76 carried by a pair of plates 78 secured to and extending below the platform 66. A ratchet wheel 80 is secured to the sprockets 74.

One end of a chain 82 is rigidly secured in a side wall 61 near the top of the pit 60. The other end of chain 82 is anchored at the bottom of the pit diagonally across from the upper end of that chain. Intermediate its ends the chain 82 passes in meshing engagement with one of each pair of sprockets 68 and 74. Similarly, one end of a second chain 84 is rigidly secured in a side wall 61 near the top of the pit 60 at a point opposite the upper end of the chain 82. The other end of chain 84 is anchored at the bottom of the pit opposite the point of anchorage of the lower end of chain 82. Intermediate its ends the chain 84 passes in meshing engagement with the other of each pair of sprockets 68 and 74.

As in the embodiment of Fig. 1, the platform 66 on the single post lift shown in Fig. 2, is kept horizontal despite any inequality of distribution of aload thereon.

A pawl 86 is pivotally secured to the plates 73 by a stud 811. The pawl 86 is engageable with the ratchet wheel 80, and when so engaged serves to lock the chains 82 and 84 with the sprocket wheels 68 and 74 and to prevent downward movement of the platform 66.

Integral with one end of a handle 96, and extending in a line at right angles thereto, are arms 92 and 94. The handle 90 pivots on a stud 91 which is secured to one of theplates 78. The handle 96 is frictionally held in position on the stud 91 by a friction washer 95 and nut 96 fixedto the projecting end of the stud as shown in Fig. 2. Stop studs 98 and 100, secured to the plate 78, limit the extent of downward movement, respectively, of arms 92 and 94. The stop stud 100 serves also to limit upward movement of the pawl 86. A tension coil spring 102 connects the pawl 86 with the handle arm 94.

The frictional resistance to movement of the handle 90 produced by the washer 95 held against the handle by the nut 96 is sufficient that the handle cannot be moved by the force applied to it due to the tension in the spring 102' when the handle is in the position shown and the pawl is in engagement with the ratchet wheel 86. A vertical bar 104 is fixed solidly on the bottom of the pit 60 at such a point that when the platform 66 nearly reaches its lowermost level, the arm 92 will engage the upperend of the bar 104 and cause the handle 96 to swing clockwise and thereby permit the pawl 86 to fall into engagement with the ratchet wheel 80. Consequently, upon the next upward movement of the lift, the pawl 86 will ride over the teeth of the ratchet wheel 80, but will engage therewith to effect a locking of the lift against any accidental downward movement thereof.

When the lift is to be lowered, the handle 90 is swung counterclockwise to the position in which it is shown in full lines in Fig. 2, to pull the pawl away from the ratchet wheel. If there has been some leakage of hydraulic fluid from the system, the pawl 86 may be carrying th e load, and thus be firmly engaged with ratchet Wheel- 80. Under the latter conditions, the spring 102 will be tensioned and the handle 99 will remain in the position shown in Fig. 2, due to its frictional mounting. The operator must then operate the control valve to raise the platform a suflicient distance to free the pawl from the ratchet wheel, whereupon the spring 102 will raise the pawl to the position in which it is shown in Fig. 2. The lift may then be lowered by opening acontrol valve to permit escape of fluid from the cylinder 62.

The means for maintaining the platform of a lift level as it is elevated and lowered, may comprise a rack and pinion arrangement. As shown in Fig. 3, a two-post lift having. plungers 119 and 111, have head members 112 and 113 respectively, to which racks 114 and 115' are secured, and upon which a platform 169 is mounted. These racks mesh respectively with pinions 118 and 119 secured to the ends of a shaft 126 which is mounted for rotary movement in suitable journal bearings 122, 1 23. A ratchet wheel 126 is keyed to the shaft 120 and is adapted to be engaged by a bellcrank-shaped pawl 128 (Fig. 4) suitably pivoted on a bracket 130 secured to a pit cover 132. A rod 134' is connected to the pawl 128 by a spring 129 and extends through the pit cover 132, there being a" suitable friction fitting 136 applying sufficie'nt friction to hold the rod and the pawl in an elevated position. A handle 138 is secured to the upper end of the rod 134.

The embodiment of the invention shown in Figs. 3 and 4 operates in the same general manner as the previously described forms of the invention in that, within the limits of the torsional strength of the shaft 120, the platform 109 will remain level regardless of the position of 4. the load thereon. As in the other embodiments, if leakage occurs the pawl 12% and ratchet 126 will prevent rotation of the shaft and thus prevent accidental lowering of the platform.

When the lift platform is to be lowered, the pawl is disengaged from the ratchet wheel by pulling upwardly on the handle 138. In the event that there has been some accidental leakage of hydraulic fluid from the system, the pawl may be locked in engagement with the ratchet wheel because of the fact that it is, in effect, carrying the load. Under these conditions the spring 129 is tensioned, it being understood that the friction applied to the rod 134 by the friction fitting 136, is sufficient to resist the tensional force of the spring 129. The lift may then be elevated a short distance, whereupon the spring 129 will free the pawl 12% from the ratchet wheel 126, and the lift may then be lowered. When the lift reaches its lowered position, a part of the platform 109 will strike the handle 138 and push the rod 134 downwardly, and thereby permit the pawl 128 to fall into engagement with its ratchet wheel 126.

The rack and pinion type of equalizing mechanism may also be employed in the single post type lift shown in Figs. Sand 6, in which the load is transferred between floors 144 and 146. In this form of the invention, a pair of racks 148 and 149 are suitably embedded in the building walls or foundation, and are engaged by pinions 156 and 151, respectively, which are keyed to the end of a shaft 154; The shaft 154 is mounted in suitable bearings 156 carried by brackets 158 welded to a platform 16-0 and to a beam 162. The beam 162 is secured to the head of a plunger 164 reciprocable in a cylinder 166. A ratchet wheel is keyed to the shaft 154, and, as shown in Fig. 6, is adaptedto be engaged by a pawl 172 pivotally mounted on one of the brackets 158. The pawl is connected to one arm 174 of a three-armed lever 1'76 mounted for rotation on a bolt 178, there being a friction washer clamped between the head of the bolt 178 and the lever 176. The arm 174 is connected to the pawl 172* by a tension spring 182. The second arm 184 of lever 1 76 serves as-a handle, while the third arm 136 thereof is adapted to be engaged by the end of an abutment 188 as the lift approaches its completely lowered position, thereby to swing the lever 176 counterclockwise and permit the pawl 172 to reengage its ratchet wheel 170. The form of the invention shown in Figs. 5 and 6 operates substantially the same as the embodiment shown in Fig. 2.

From the foregoing it' will appear that I have provided, in combination with a hydraulically operated lift, coac'ting means for maintaining the lift platform horizontal, regardless of the distribution of load thereon and for preventing accidental lowering of the lift due to leakage of the hydraulic fluid or air from the lift cylinder.

It will be understood that in some installations the equalizer may be constructed of equivalent wire cables and sheaves instead of chains and sprockets. By the terms pawl and ratchet, I wish to include not only the conventional type shown, but also those of the wedge and roller type sometimes used as unidirectional driving clutches. Similarly, each chain may be replaced by one or more wire ropes, in which case the sprockets would be replaced by sheaves. I prefer to use chains whenever the lift is designed for handling heavy loads.

While I have shown and described preferred embodiments of my invention; it will be apparent that variations and modifications thereof may be made without departin'g from the underlying principles of the invention. I therefore desire; by the following claims, to include within the scope of the-invention all such variations and modifications by which substantially the results of my invention may be' obtained through' the use of substantially the same or equivalent means.

I claim:

1. In a lift having a vertically movable load support, and means for raising and lowering it, the combination of two pairs of sprockets mounted for rotation below the opposite err is of the load support, the sprockets of one pair being secured together, a ratchet wheel connected for rotation with one of said last named sprockets, a pair of chains to insure translational movement of said support, each chain having one end anchored above one pair of sprockets, meshing with one sprocket of each pair, and having its opposite end anchored below the other pair of sprockets, a gravity actuated pawl adapted for engagement with the ratchet wheel to prevent rotation thereof in the direction it rotates as the load support is lowered, manually operable means for effecting disengagement of the pawl from the ratchet wheel, and abutment means for freeing the pawl for gravity movement as an incident to movement of the load support to the end of its ordinary downward movement thereby to permit gravity actuated movement of the pawl and its engagement with the ratchet wheel so as positively to hold the load support against further downward movement.

2. In a lift mechanism having a vertically movable load support and means for raising and lowering it, the combination of two pairs of sprockets mounted on the underside of the load support at opposite ends thereof, the sprockets of one pair being secured together, a ratchet wheel connected for rotation with one of said last named sprockets, a pair of chains to insure translational movement of the support, each chain having one end anchored above one pair of sprockets, meshing with one sprocket of each pair, and having its opposite end anchored below the other pair of sprockets, a gravity actuated pawl adapted for engagement with the ratchet wheel to prevent rotation thereof in the direction it rotates as the load support is lowered, a hand lever pivotally mounted on the load support and connected to the pawl and movable between a first position to effect disengagement of the pawl from the ratchet wheel and a second position in which the pawl is permitted gravity movement to engage the ratchet wheel, means frictionally restraining the hand lever against free swinging movement thereof but permitting the lever to be moved upon application of a positive external force thereto, and abutment means engageable with and adapted to move the hand lever to said second position for freeing the pawl for gravity movement as an incident to movement of the load support to the end of its ordinary downward movement thereby to permit gravity actuated movement of the pawl and its engagement with the ratchet wheel so as positively to hold the load support against further downward movement.

3. In a lift mechanism having a load support and means for raising and lowering it, the combination of two pairs of sprocket wheels mounted for rotation at the opposite ends of the load support, the wheels of one pair being rigidly connected together, a pair of long chains to insure translational movement of said support; each chain having one end anchored above one pair of said wheels, passing around one or" each pair of wheels, and having its other end anchored below the other pair of Wheels; a ratchet wheel rigidly connected to the rigidly connected pair of sprocket wheels, a pawl cooperable with the ratchet wheel to prevent rotation thereof in the direction it rotates as said load support is lowered, and manually operable means for elfecting disengagement of the pawl from the ratchet wheel.

4. The combination set forth in claim 3, in which the sprocket wheels are mounted for rotation on fixed axes below floor level, in which abutment means are provided to engage the pawl when the load support reaches the end of its ordinary downward movement for eiiecting engagement of the pawl with the ratchet wheel, and in which the manually operable means for efiecting disengagement of the pawl from the ratchet wheel includes a handle and a spring tension transmitting member interconnecting the handle and the pawl to permit manual movement of the handle reln: ive to the pawl to pawl disengaged position, so that when the load transmitted from the support through the sprocket wheels and ratchet wheel. to the pawl is released the spring tension transmitting member will disengage the pawl from the ratchet wheel.

5. In a hydraulic lift mechanism having a cylinder, a plunger reciprocable in the cylinder, and a load support carried by the plunger, the combination of a pair of rotary elements mounted for rotation below each end of the load support and carried thereby, one of said rotary elements constituting a sprocket wheel, a pair of flexible tension members to insure translational movement of the support, each tension member having one end anchored above one pair of rotary elements when the load support is at its normally uppermost level, each tension member being trained around one of each pair of rotary elements and having its other end anchored below the other pair of rotary elements when the load support is at its normally lowermost level, one of said tension members constituting a chain trained around said sprocket wheel in nonslip engagement therewith, a ratchet wheel rigidly connected to the sprocket wheel for rotation therewith, a gravity actuated pawl cooperable with the ratchet wheel to prevent rotation thereof in the direction it rotates as the load support is lowered, manual- 1y operable means for effecting disengagement of the pawl from the ratchet wheel and for holding the pawl in disengaged position, and means cooperable with the manually operable means as an incident to the approach of the load support to the lower end of its ordinary downward movement to release the pawl from disengaged position thereby to permit gravity movement of the pawl into engagement with the ratchet wheel so as to prevent further downward movement of the load support.

6. The combination set forth in claim 5, in which the manually operable means for effecting disengagement of the pawl from the ratchet wheel is a three-armed, limitedly rotatable handle mounted on the load support, one arm of the handle being attached to the pawl by a spring to withdraw the pawl from engagement with the ratchet wheel when said arm is moved in one direction, in which friction means is mounted on the load support in frictional engagement with said handle to yieldably hold the latter against swinging movement by the spring, and in which the means cooperable with the manually operable means is a fixed stop positioned to be engaged by another arm of said handle to move the handle in the opposite direction when the load support nearly reaches its lowermost level, thereby releasing the pawl for gravity movement.

7. In the combination set forth in claim 2, a tensioned resilient means connecting the pawl actuating hand lever and the pawl to permit movement of the lever from said second position to said first position thereby to condition the pawl for movement out of engagement with the ratchet wheel when the load transmitted from the support through the sprockets and ratchet wheel to the pawl is released, the force exerted by the tensioned resilient means being insutficient to overcome the force of the means frictionally restraining the hand lever against free swinging movement.

References Cited in the tile of this patent UNITED STATES PATENTS 1,168,935 Davidson Jan. 18, 1916 1,470,581 Dutty Oct. 9, 1923 1,710,442 Warshaw -r Apr. 23, 1929 2,593,630 Thompson Apr. 22, 1952 FOREIGN PATENTS 59,475' Norway June 13, 1938 

